In recent years, a terminal device such as smartphone, tablet PC, game machine, cellular phone etc. is being put into practical use, wherein a flexible display panel, e.g. organic EL panel, LED panel, etc. is provided to cross both a first casing and a second casing, so that the flexible display panel is bent into twofold while out of use, and that it is unfolded into a single plane in use. For such a terminal device, an example of an opening and closing device for flexibly coupling a first casing and a second casing is disclosed in JP Laid-Open Patent Application No. 2014-161009.
In an opening and closing device according to JP Laid-Open Patent Application No. 2014-161009, a first casing and a second casing are flexibly coupled by resin bellows structure to support an organic EL panel. Still further, when the first casing and the second casing overlap each other and the organic EL panel is bent into a folded state, the opening and closing device forms a curvature in the shape of cylindrical surface to give the organic EL panel a predetermined curvature radius. Furthermore, in the opening and closing device according to JP Laid-Open Patent Application No. 2014-161009, a reinforced beam made of shape-memory alloy is provided in curving direction so as to cross the resin bellows structure. The reinforced beam can be freely plastically deformed to maintain its shape, so that the first casing and the second casing can be held at any opening angle.
In an opening and closing device, wherein a first casing and a second casing are coupled to support a flexible display panel, it is preferable to be able to realize a curvature at a predetermined curvature radius, when the flexible display panel is bent into a folded state. This is because some properties of the flexible display panel may be impaired by folding it to a curvature radius smaller than what is acceptable. Furthermore, in the opening and closing device, a bending surface supporting the flexible display panel preferably has a constant length as accompanied by a bending/unfolding of the flexible display panel. This is because some properties of the flexible display panel may be impaired by a remarkable fluctuation in a length of the bending surface as accompanied by the bending/unfolding, which results in excessive force acting on the flexible display panel. Furthermore, in the opening and closing device, the first casing and the second casing supporting the flexible display panel can be preferably held at any opening angle. If the opening and closing device itself has a function of holding the unfolding (it is also referred to as opening and closing) angle, it can maintain a state of the flexible display panel being bent into twofold or unfolded into a single plane, even without hold on the flexible display panel by hands or tool.
However, a resin bellows structure as disclosed in JP Laid-Open Patent Application No. 2014-161009 has a different length in a closed state when the first casing and the second casing overlaps each other, from an opened state when the first casing and the second casing are unfolded to form a plane. In this manner, if the flexible display panel is supported on bending parts of the bellows structure, a tension force is applied on the flexible display panel in its closed state, while a gap is generated between the flexible display panel and the bellows structure in its opened state.
To this end, another opening and closing device has been proposed, wherein a plurality of link members are coupled so as to be slidable with rotation in a bending direction, and wherein an arc-shaped bending surface is formed by an enveloping surface inside the plurality of link members. Still further, it has been further proposed that a coupling portion for adjacent link members is tightly fitted to generate a friction force, such that the first casing and the second casing can be held at any opening angle.
However, if a coupling portion for adjacent link members undergoes an interference fit, a mechanism including such cannot be a link mechanism, the adjacent link members cannot smoothly slide relative to each other in a bending direction, so that the entire plurality of link members cannot smoothly generate a bending or release from bending.